The invention finds applicability in 1,1,1,3,3-pentachloropropane production.
There is a need in industry to produce halohydrocarbons that are environmentally safe as a replacement for certain halogenated chemicals that deplete the ozone layer.
Prior Art
1,1,1,3,3-Pentachloropropane (HCC240f) can be obtained by the addition reaction of carbon tetrachloride and vinyl chloride. For example, Kotora et.al. (Journal of Molecular Catalysis, Vol.77, 51-60 (1992)) added carbon tetrachloride to vinyl chloride in a batch reaction using either cuprous chloride or tetrakis(acetonitrile)copper(I) perchlorate catalyst and n-butylamine as co-catalyst. They obtained about a 97-98% yield by these methods. Zil""berman et.al. (J.Org.Chem.USSR (Engl.Transl.), Vol. 3, 2101-2105 (1967) CAS [68(10):40147p]) used a ferrous chloride hydrate catalyst with isopropanol solvent to make a product mixture containing only 81 wt % HCC240f, together with several higher molecular weight telomers. Both of these batch methods involved aqueous wash steps for the product purification. Neither method is adaptable to a continuous process in which the catalyst is to be recycled.
Rygas et.al. (U.S. Pat. No. 5,902,914, May 11, 1999) described a continuous process for the production of haloalkanes, including HCC240f, which includes catalyst recycle and purification steps. For example, carbon tetrachloride and vinyl chloride are (A) reacted in the presence of a catalyst and a cocatalyst to produce a haloalkane product stream. This stream is (B) flash-distilledxe2x80x9d to produce a first stream comprising unreacted feed material and the cocatalyst and a second stream containing a haloalkane product and the catalyst. The second stream from (B) is then (C) filtered to remove the catalyst, and the filtrate is (D) distilled to purify the haloalkane product. Step (D) may be carried out in the presence of metal chelating agents, such as tributylphosphate, which may act to improve the distillation yield. Their preferred catalyst/cocatalyst systems were cuprous chloride/tert-butylamine or iron powder/hexamethylphosphoramide.
However, this scheme will not work for the catalyst system described herein. In our invention, the catalyst is ferrous chloride (produced in situ from the reaction of ferric chloride and iron metal), and the cocatalyst is tributylphosphate. Tributylphosphate, being a very high-boiling substance, will not go overhead in a flash distillation such as step (B) of Rygas et.al. Further, a filtration step such as step (C) is of no value for our system, since the catalyst components ferrous chloride and ferric chloride are soluble in the reactor effluent, and even more soluble in the bottoms stream from an initial distillation step.
Rygas et.al. (U.S. Pat. No. 6,187,978 Feb. 13, 2001) have also described another process for the production of haloalkanes. For example, they disclose a process in which carbon tetrachloride may be reacted with vinyl chloride in the presence of an iron-containing compound and tributylphosphate to produce a product stream. Then, in separation scheme (A), the reactor product stream may be distilled into a top stream comprising volatile reactants that are recycled, and a bottom stream that contains the HCC240f product and the catalyst complex. This bottom stream may be further distilled into a second top stream comprising the desired product, and a second bottom stream containing the catalyst complex, which is recycled. Alternatively, in separation scheme (B), the reactor product stream may be distilled into a top stream that contains the desired product and a bottom stream that contains the catalyst components. This bottom stream may be recycled, while the top stream may be distilled into a second top stream containing volatile reactants, which are recycled, and a second bottom stream, which contains the desired halocarbon product.
But separation scheme (A) would subject the catalyst components to two distillation steps before they are recycled into the reactor. Each distillation step stresses the catalyst components, causing degradation. In a process based on the reaction of carbon tetrachloride with vinyl chloride in the presence of iron chlorides and tributylphosphate, such as that described herein, the catalyst degrades by a process of chemical reactions that increase in extent with temperature, time, and catalyst concentration. The bottoms stream from the first distillation of scheme (A) is large, since it contains the desired product of the reaction. This means that the equipment used for both distillation steps of scheme (A) must be large, and the residence times in both stills must be relatively long. The catalyst components are recovered as the bottoms from the second still, where the temperature is high, the catalyst concentration is high, and the liquid residence time is long.
Separation scheme (B) is better, since the catalyst is recovered and recycled as the bottoms from the first tower. Even so, this first tower is necessarily large, since it handles the whole product load, going overhead, and so the liquid residence time is long. If one wishes to recover most of the product, then the concentration of catalyst components in the bottoms of the first tower is high, and the temperature is high. These conditions again promote rapid degradation of the catalyst. Furthermore, the reaction of the invention results in the production of two main undesired byproductsxe2x80x941,1,1,3,5,5-hexachloropentane (HCC470jfdf) and 1,1,3,3,5,5-hexachloropentane (HCC470nfaf). These components, being less volatile than the desired HCC240f (b.p. 179 C), tend to stay with the catalyst components, which are either non-volatile, or have very high boiling points (tributylphosphate boils at 289 C.). Therefore, if the bottoms of the first tower are recycled, this stream carries with it a considerable amount of the hexachloropentane byproducts. These components, in the recycle stream, are harmful to the desired reaction in two ways: first, they dilute the reactants, thereby reducing the reaction rate. Second, they can react with vinyl chloride, thus consuming valuable feedstock, and produce further undesired by-products.
What is needed is a method of recovering the HCC240f, free of the hexachloropentane byproducts, which minimizes the stress placed on the catalyst components, and which separates, as much as possible, the catalyst components from the hexachloropentanes.
Wilson et al (U.S. Pat. No. 6,313,360) is directed to a process for the production of 1,1,1,3,3-pentachloropropane by reacting carbon tetrachloride (CCl4) and vinyl chloride in the presence of a catalyst mixture (organophosphate solvent, iron metal and ferric chloride). The process of the herein disclosed invention in superior to that of the Wilson et al in that the conditions employed are more economic and the activity of the catalyst is maintained to a far greater degree.
The prior art (Wilson et al) describes a single-stage catalyst recovery system. In prior art processes high temperature and long residence time tend to cause degradation of the catalyst. The inventors have found that by adding a second distillation step and modifying the conditions of the first distillation step a surprisingly high percentage of the desired product (1,1,1,3,3-pentachloropropane) can be recovered in pure form and the catalyst is maintained in exceptionally useful form.
The inventors have succeeded in producing a much more highly concentrated catalyst recycle stream than that embodied in U.S. Pat. No. 6,313,360. They have also succeeded in recovering a significantly higher percentage of the 1,1,1,3,3-pentachloropropane produced. Based on the prior-art work, in lab and pilot plant, the inventors have unexpectedly retained significant amounts of active catalyst in their recycle process.
A main object of the invention is to produce a process that will maximize the recovery of the catalyst.
A further object of the invention is to perform the process under relatively mild conditions.
A significant object of this invention is to provide a process for producing halohydrocarbons under economic conditions.
Another object of this invention is to produce a haloalkane production process that preserves the catalyst.
These and other objects of the present invention will become apparent from a reading of the following specification taken in conjunction with the enclosed drawings.
The herein disclosed invention provides an improved method for catalyst recovery and recycle and for product recovery in a high capacity continuous process for the manufacture of a desired haloalkane product by the addition reaction of a haloalkane with a haloalkene, in the presence of a catalyst system comprised of ferrous chloride, ferric chloride, and a trialkylphosphate. The catalyst components tend to degrade when stressed by high temperature, long residence times, and high concentrations. The instant invention mitigates this problem. The catalyst components are recovered in a two-stage distillation system, in which the first stage performs a rough cut separation between the catalyst components and the desired product, under relatively mild conditions that do not stress the catalyst components unduly, and the second stage performs a more nearly complete separation between the catalyst components and the desired product, using relatively small equipment and short residence time, to stress the catalyst components as little as possible, given the relatively higher temperature and concentration of the catalyst components in this unit.
The starting materials for carrying out the process of the instant invention are carbon tetrachloride (CCl4), and vinyl chloride in the presence of a catalyst system comprised of ferric chloride, ferrous chloride, and metallic iron in a trialkylphosphate solvent, tributylphosphate being the preferred trialkylphosphate solvent. While1,1,1,3,3-pentachloropropane is the principle and desired product produced, other byproducts such as 1,1,1,3,5,5 hexachloropentane, 1,1,3,3,5,5 hexachloropentane and hexachloroethane are also produced.
A preferred method for preparing 1,1,1,3,3-pentachloropropane is described. Vinyl chloride and carbon tetrachloride are reacted in the presence of tributylphosphate and iron metal in the reactor and a reactor effluent containing halohydrocarbons and catalyst components are sent to the first refluxed evaporator. In the first refluxed evaporator, the reactor effluent is split into distillate and bottom fractions. The distillate contains mainly 1,1,1,3,3-pentachloropropane produced and lower boiling compounds from a heavy bottom fraction. The bottom fraction contains a small fraction of the 1.1.1.3.3-pentachloropropane produced, and higher boiling materials, including catalyst components. Serious degradation of catalyst components is avoided by operating the evaporator under partial vacuum at a relatively low bottom boiling temperature and at a fairly short liquid residence time. The second refluxed evaporator removes most of the remaining 1,1,1,3,3-pentachloropropane from the bottom liquid from the first evaporator, producing a new bottom fraction containing the catalyst components in a form highly suitable for recycle to the reactor. Serious degradation of the catalyst in this tower is avoided by operating at low temperature, and at even lower liquid residence time than in the first tower.
In its broadest aspect, the herein disclosed invention involves a process for preparing a desired haloalkane, as for example, 1,1,1,3-tetrachloropropane, 1,1,1,3,3,3-hexachloropropane or 1,1,1,3-tetrachlorobutane by contacting a haloalkene or alkene, such as, vinylchloride, ethylene, propylene, butylene or 1,1-dichloroethylene with a haloalkane such as carbon tetrachloride, chloroform or 1,1,1-trichlorethane in the presence of effective amounts of catalyst components, ferrous chloride, ferric chloride, and a trialkylphosphate compound, under conditions effective to promote an addition reaction and to form a product stream containing said haloalkane product, higher boiling haloalkane byproducts, unreacted feedstocks, and catalyst components, and separating the desired haloalkane product from the high-boiling undesired haloalkane byproducts and the catalyst components using a two-stage catalyst recovery unit (CRU), wherein, the bottom fraction from the first stage flows into the second stage, and the overhead fractions from the two stages are combined for further purification steps, and the first stage of the CRU recovers, in the distillate, between 50 and 90% of the desired haloalkane product contained in the reactor effluent, leaving more than 98% of the high-boiling undesired haloalkane byproducts in the bottom fraction, and the second stage of the CRU recovers, in the distillate, more than 70% of the remaining desired haloalkane product, leaving more than 98% of the high-boiling undesired haloalkane byproducts in the bottom fraction, together with the catalyst components, and recycling most of the bottom fraction from the second stage of the CRU to the reactor, and purging a small fraction of it from the system to control byproduct concentrations in the reactor and to avoid excessive catalyst degradation. In the process the first stage of the CRU roughly distills the desired haloakane product and lower boiling components from the undesired high boiling haloalkane byproducts, higher boiling components, and catalyst components, producing a bottom fraction containing between 35 and 75 percent of the desired haloalkane product and wherein the second stage further separates the bottoms stream from the first stage into an overhead stream containing the desired haloalkane product and less than 2 wt. percent of the undesired high-boiling haloalkane byproducts, and produces a bottoms catalyst fraction suitable for recycle to the reactor, which contains less than 25 wt. percent of the desired haloalkane product. The first stage of the CRU can be operated at 10 to 50 Torr bottom pressure, and at 160-240 degrees F. bottom temperature, and the liquid residence time, defined as the ratio of the volume of liquid contained in the bottom of the tower to the volumetric liquid flow rate from the bottom of the tower, is less than five days, and the second stage of the CRU is operated at 3 to 15 Torr bottom pressure, and at 180-260 degrees F bottom temperature, and the liquid residence time is less than 12 hours. More specifically, the first stage of the CRU can be operated at less than 215 F. bottom temperature, and at less than five days liquid residence time, and the second stage of the CRU is operated at less than 240 F. bottom temperature, and at less than 12 hours liquid residence time. Note, also, that under specific conditions, the first stage of the CRU can be operated at 10 to 50 Torr bottom pressure, and at 160-240 F. bottom temperature; the second stage of the CRU can be operated at 3 to 15 Torr bottom pressure and at 180-260 F. bottom temperature; the first stage of the CRU can be operated at less than 215 F. bottom temperature, and the second stage of the CRU can be operated at less than 240 F. bottom temperature; the liquid residence time in the first stage is less than five days and the liquid residence time in the second stage is less than 12 hours; the liquid residence time in the first stage is less than 24 hours and the liquid residence time in the second stage is less than six hours; the liquid residence time in the second stage is no more than 20% of the liquid residence time of the first stage, and the temperature of the second stage bottom liquid is no more than 25 degrees F. hotter than the temperature of the first stage bottom liquid. In a specific embodiment of this invention, the desired haloalkane product is 1,1,1,3,3-pentachloropropane, the haloalkene feedstock is vinyl chloride, the haloalkane feedstock is tetrachloromethane, the main undesired high-boiling haloalkane byproducts are 1,1,1,3,5,5-hexachloropentane and 1,1,3,3,5,5-hexachloropentane, and the trialkylphasphate compound is tributylphosphate. In a special aspect of the invention, there is carried out a process for preparing 1,1,1,3,3-pentachloropropane comprising, (a) reacting carbon tetrachloride and vinyl chloride in the presence of a catalyst, and then (b) distilling the reaction products of step (a) using temperature and pressure conditions that do not materially destroy the catalyst and also produce a significant amount of 1,1,1,3,3-pentachloropropane. More specifically the invention encompasses a method for generating 1,1,1,3,3-pentachloropropane comprising, (a) reacting carbon tetrachloride with vinyl chloride in the presence of a catalyst comprising elemental iron, ferric chloride, and tributylphosphate, producing a reactor effluent, and (b) distilling the reactor effluent, separating 1,1,1,3,3-pentachloropropane and lower boiling components from high boiling components at a temperature and pressure which do not substantially inactivate the catalyst, and producing a bottom fraction containing the catalyst components and less than 50% of the 1,1,1,3,3-pentachloropropane contained in the reactor affluent from step (a), and (c) distilling the bottom fraction from step (b) to recover overhead at least 70% of the 1,1,1,3,3-pentachloropropane remaining in the bottom fraction from step (b), and producing a new bottom fraction suitable for recycle to the reactor, and (d) combining the distillate fractions of steps (b) and (c) for further purification of the 1,1,1,3,3-pentachloropropane product. Also, envisioned by this invention is a method for producing a purified halohydrocarbon and a catalyst recycle stream comprising (a) reacting carbon tetrachloride and an olefin in the presence of a catalyst to prepare a mixture of a desired halohydrocarbon and catalyst, (b) processing the desired halohydrocarbon and catalyst in a first refluxed evaporator employing a partial vacuum and moderate temperature effective to prevent excessive catalyst degradation, recovering a substantial fraction of the desired halohydrocarbon overhead, and producing a bottom fraction containing the catalyst components, (c) processing the bottom fraction from step (b) in a second refluxed evaporator employing a partial vacuum, moderate temperature, and shortened liquid residence time effective to prevent excessive catalyst degradation, recovering a substantial fraction of the remaining desired halohydrocarbon overhead, and producing a bottom fraction containing the catalyst components in a state suitable for substantial recycle to the reactor, and (d) further processing the combined overhead fractions from the first and second refluxed evaporators of steps (b) and (c) to produce a purified halohydrocarbon stream. The purified halohydrocarbon recovered is 1,1,1,3,3-pentachloropropane, and the olefin fed is vinyl chloride. The first refluxed evaporator is operated at about 10 to 50 Torr, with a bottom temperature of about 160 to 240 F., and the second refluxed evaporator is operated at about 3xcx9c15 Torr, with a bottom temperature of about 180-260 F. The liquid residence time in the first refluxed evaporator is less than 24 hours and the liquid residence time in the second refluxed evaporator is less than about six hours. The first refluxed evaporator has a pressure of about 20 Torr and a temperature of about 187 F., and the second refluxed evaporator has a pressure of about 5 Torr, and a temperature of about 207 F. An elegent embodiment of the invention involves a process for preparing a desired haloalkane produce comprising: (a) contacting a haloalkene and a haloalkane feedstock in the presence of effective amounts of catalyst components ferrous chloride, ferric chloride, and a trialkylphosphate compound, under conditions effective to promote an addition reaction and to form a reactor effluent containing said haloalkane product, higher boiling haloalkane byproducts, unreacted feedstocks, and catalyst components, and (b) separating the desired haloalkane product from the high-boiling undesired haloalkane byproducts and the catalyst components using a two-stage catalyst recovery unit, wherein, (i) the bottom fraction from the first stage flows into the second stage, and (ii) the first stage of the CRU recovers, in the distillate, between 50 and 90% of the desired haloalkane product contained in the reactor effluent, leaving more than 98% of the high-boiling undesired haloalkane byproducts in the bottom fraction, and (iii) the second stage of the CRU recovers, in the distillate, more than 70% of the remaining desired haloalkane product, leaving more than 33% of the high-boiling undesired haloalkane byproducts in the bottom fraction, together with the catalyst components, and (iv) further distilling the overhead fraction from step iii. to produce a new overhead fraction containing the desired haloalkane product and less than 1 wt. % of the high-boiling undesired haloalkane products and a new bottom fraction containing the undesired haloalkane produce, and (v) disposing or otherwise using the bottom fraction of step iv., and (c) combining the overhead fraction of step iv. with the overhead fraction of step ii. for further purification, and (d) recycling most of the bottom fraction from step iii. to the reactor, and purging a small fraction of it from the system to control byproduct concentrations in the reactor and to avoid excessive catalyst degradation.